Luminance artifacts of cathode-ray tube displays for vision research.

Phosphor persistence, video bandwidth, DC restoration and high-voltage regulation affect the appearance of images presented on cathode-ray tubes (CRTs), potentially resulting in differences between nominal and actual stimuli. We illustrate these effects by measuring physical parameters of horizontal and vertical static and counter-phase flickering gratings, and we illustrate problems for vision research by measuring contrast sensitivity to these gratings. We also measured the extent to which calibration protocols actually result in the monitor being calibrated over its entire area regardless of image size. The results of our physical measurements indicate substantial differences between gratings that nominally differ only as to orientation. Consistent with these differences, our psychophysical measurements indicate different sensitivities when the bars of the gratings are parallel or orthogonal to raster lines, regardless of the retinal orientation of the gratings. The results of our calibration check show that only a small region around the target area of calibration can be regarded as effectively linearized, and only if the size of the test image used during the check is similar to the size of the calibration patch. Overall, our results indicate potentially severe problems with the use of CRTs in vision research, and we discuss some published results that are likely to have been affected by these problems.     

Studies on the simultaneous production of single cell protein and polygalacturonase fromKluyveromyces fragilis

Summary Kluyveromyces fragilis produces polygalacturonase (PG) on a lactose medium. Although the enzyme is normally repressed at high aeration levels, significant amounts of PG can be produced under such conditions when pectin is added as inducer. The productivity and yield of cell mass were not significantly affected by the presence of inducer, suggesting potential applications to current single cell protein processes from whey.     

Long-wavelength fluorescence of tyrosine and tryptophan solutions

We report in this paper the presence of fluorescence bands of tryptophan and tyrosine solutions centered above 550 nm. This long-wavelength fluorescence is of much lower intensity, (0.4-2.7)%, than the UV fluorescence of these aromatic aminoacids. The basic characteristic of these fluorescence bands are: (a) tyrosine: lambda em = 600 nm with two excitation peaks centered at 453 nm and 550 nm (b) tryptophan: lambda em = 675 nm with two excitation peaks centered at 455 and 560 nm. It has been found that irradiation of tyrosine solutions with a potent UV lamp promotes an important increase of absorption at 310 nm and above 400 nm.     

Molecular characterization of human platelet glycoproteins IIIa and IIb and the subunits of the latter

Sedimentation equilibrium and low-angle laser-light scattering were used to determine the molar mass of the glycoprotein moieties in the complexes of sodium dodecyl sulphate with the human platelet membrane glycoproteins IIb (GPIIb), IIIa (GPIIIa), and the (GPIIb) and (GPIIb) subunits of GPIIb. The values obtained by both procedures, except those for GPIIb, agree within experimental error with those calculated from their chemical composition: GPIIb (114,000 g mol^-1), GPIIb (22,200 g mol^-1), and GPIIIa (91,500 g mol^-1). The molar mass of GPIIb determined by light scattering (142,000 g mol^-1) and sedimentation equilibrium at different solvent densities (134,000 g mol^-1) also agree, within experimental error, with the values calculated either from its chemical composition (136,500 g mol^-1) or from the sum of the molar masses of its subunits. However the molar mass determined by sedimentation equilibrium at constant solvent density, is consistently underestimated (116,000 g mol^-1).High-performance size-exclusion chromatography in sodium dodecyl sulphate solutions overestimates the molar mass of these glycoproteins and their Stokes radii, and therefore the maximal frictional ratios derived from them.Abbreviations GPIIb glycoprotein IIb - GPIIIa glycoprotein IIIa - GPIIb and GPIIb and subunits of GPIIb, respectively - CM-GPIIb CM-GPIIb, and CM-GPIIIa, totally reduced and carboxymethylated forms of GPIIb, GPIIb, and GPIIIa, respectively - SDS sodium dodecyl sulphate - eosin-ITC eosin-5-isothiocyanate     

Physiological activity of immobilized cells of Claviceps fusiformis during long-term semicontinuous cultivation

Summary The 550-day semicontinuous cultivation of Claviceps fusiformis immobilized in calcium alginate is documented. The vegetative mycelium from seed or from early-production submerged culture is the best choice for immobilization. No extracellular glucans are produced by immobilized cells. Immobilized spores give low yields of clavine alkaloids. Alginate concentrations in a range of 2%–4% do not influence yield and spectrum of alkaloids. The cytoplasm of the immobilized cells becomes condensed (after 3 days), polysaccharides disappear, and centres of lipid synthesis are formed in the cytoplasm. After 60 days the cells harbour a great number of lipid particles, mitochondria are diminishing and their cristae partly disappear, indicating a decreased respiration capacity. After 350–500 days the volume of most cells is increased many times and the cells are filled with large oval bodies of electrondense material. Chloramphenicol protects immobilized cultures against bacterial contamination.     

On the preservation of avian blood cells

The functional state of erythrocytes from hen during their conservation with a preserving solution for 24 days at 4 degrees C, has been estimated by studying some biochemical and hemorheological parameters. Results show an initial phase in the preservation period (4-5 days) in which red blood cells maintain their values at levels similar to those at the beginning of the experience, except for osmotic resistance. Furthermore a progressive erythrocyte deformability loss, linked to ATP depletion (with rise in inorganic phosphate levels) as well as a gradually higher rate of hemolysis, were detected.     

Action of mercury on sugar transport across rat small intestine, in vivo

Absorption of galactose from in vivo perfused rat jejunum was inhibited by 0.1-0.5 mM Hg2+. A few minutes' delay was required for maximal inhibition values. The effects remained after saline solution washing but were in part reversed by EDTA and in higher proportion by dithioerythritol. Absorption inhibition could be ascribed to impairment of the sugar-Na phlorizin-sensitive cotransport component: The passive apparently diffusional component that remains under 0.5 mM phlorizin and absorption of L-sorbose were unaffected by the metal. Hg action is explained as due to its binding to thiol and perhaps other chemical groups of proteins, at different depths in the membrane, which are directly or indirectly related to the sugar transport system.     

The action of adrenoceptor agonists and antagonists on the guinea pig and dog trachea

The action of beta- and alpha-adrenoceptor agonists (isoprenaline, orciprenaline, noradrenaline, phenylephrine and ephedrine) and antagonists (propranolol, metipranolol, exaprolol, BL 445 and phentolamine) on the resting tension and cAMP level of the guinea pig and the mechanical and electrical activities of the dog trachea were studied. By activating beta 2-adrenoceptors, isoprenaline and orciprenaline relaxed the smooth muscle, elevated the membrane potential and attenuated the excitatory effect of histamine on membrane potential and muscle tension. Noradrenaline and phenylephrine, acting on alpha 1-receptors, did not affect the membrane potential and increased the basal tension of the dog trachea only insignificantly. Ephedrine, in high concentrations, however, hyperpolarized the smooth muscle membrane and relaxed the dog trachea, while it did not alter the cAMP level in the guinea pig preparations. It is, therefore unlikely that alpha 1-adrenoceptors play a major role in the excitation of the dog trachea under resting conditions whereas the participation of alpha 2-receptors in the mechanisms of adrenergic relaxation could not be ruled out. All the beta-adrenoceptor antagonists studied enhanced the action of low isoprenaline concentrations and competitively antagonized it in high concentrations. The order of their antagonistic potency in the guinea pig trachea was as follows: metipranolol greater than propranolol = exaprolol greater than or equal to BL 445. It was suggested that metipranolol and exaprolol are nonselective beta-adrenoceptor antagonists, similarly as propranolol, whereas BL 445 shown some beta 1-selectivity. In contrast to their antagonistic effects on the membrane activities and muscle tension, both histamine and isoprenaline increased the level of cAMP in smooth muscle cells and, when present simultaneously, their effect was additive. The mechanism of histamine-induced cAMP level elevation and the possible involvement of different subcellular compartments in the action of isoprenaline and histamine in relation to the contraction-relaxation cycle is discussed.